1. Field of the Invention
The present invention relates to a class of locking pliers, or vise-grips in general, and more particularly to expander locking plier with easily adjustable clamping force. The invention is capable of clamping one or two workpieces against the internal surfaces of a tube, a fixture or another workpiece with adjustable clamping force. It is also capable to expand two portions of a workpiece or two workpieces apart by turning the rear adjustment screw mounted on the fixed arm. The screw and thread design of the jaws enable the adjustment of the invention to suit variable internal sizes of fixture or workpieces in concern.
2. Description of the Related Art
A conventional locking plier or vise-grip generally comprises a fixed arm with clamping jaw, a movable arm attached with clamping jaw and a self-locking and quick release mechanism built into the movable arm. To serve various applications, there are many different designs of the clamping jaws for locking pliers in the field, such as: cutter attachment jaws, U.S. Pat. No. 2,590,031; C-shape jaws used in the Gripping Tool, U.S. Pat. No. 2,641,149; cylindrical jaws used in tube and shaft clamping, U.S. Pat. Nos. 3,585,704 and 5,305,669; L-shape jaws used in Toe-nailing Clamping Tool, U.S. Pat. No. 4,305,575; very large gripping jaws, U.S. Pat. No. 4,386,542; chain clamping jaws, U.S. Pat. No. 4,477,937; long nose jaws, U.S. Pat. No. 4,730,524; and adjustable locking jaws, U.S. Pat. No. 5,022,290; etc. However, almost all of these designs are used to clamp externally on workpieces, or more accurately speaking, the clamping force is applied from outside towards the inside of the workpieces. Although not so common in the field, there are situations where clamping from the outside of a workpiece is not possible. Or there are applications that require the workpiece or workpieces being clamped inside a tube, or between two internal surfaces of a workpiece or fixture. Besides these static operations, there may be a situation that requires a means to expand two portions of a workpiece, or to push two workpieces apart with desired amount of force. It is the intention of the present invention to provide a handy tool to serve these purposes. Another intention is to enable the adjustment of the clamping force on the workpiece by turning the rear adjustment screw. Further intention of the present invention is to provide a convenient means to increase the expanding force on the workpieces by inserting a metal rod or any suitable screwdriver into the hole equipped on the rear adjustment screw to act as a handle to increase the turning torque. Yet another intention of the invention is to provide a simple means to adjust the workable size of the pliers. Such a simple means is the screw and thread design mounted to the jaws attached to the fixed arm and the movable arm.